Low coefficient of expansion rotors for vacuum boosters

A vacuum booster assembly comprising:

• a booster housing defining a booster chamber, the booster housing formed to include a gas inlet for allowing gas to enter the booster chamber and a gas outlet to allow gas to exit the booster chamber;
• a first rotor positioned within the booster chamber and adapted for rotation therein, the first rotor including a first shaft and at least two lobes having an outer surface that defines a first lobe profile;
• and
• a second rotor positioned within the booster chamber and adapted for rotation therein, the second rotor including a second shaft and at least two lobes having an outer surface that defines a second lobe profile,
• wherein the first and second rotors are formed from a metal including at least about 50% iron, about 20% to about 35% nickel, and about 10% to about 25% cobalt and having a coefficient of thermal expansion from about 1 (10−6 in/in*K) to about 13 (10−6 in/in*K), and wherein the outer surface of the first rotor and the outer surface of the second rotor each includes a coating including at least one of an abradable coating or a formable coating.

A vacuum booster assembly comprising:

• a booster housing defining a booster chamber, the booster housing formed to include a gas inlet for allowing gas to enter the booster chamber and a gas outlet to allow gas to exit the booster chamber;
• a first rotor positioned within the booster chamber and adapted for rotation therein, the first rotor including a first shaft and at least two lobes having an outer surface that defines a first lobe profile;
• and
• a second rotor positioned within the booster chamber and adapted for rotation therein, the second rotor including a second shaft and at least two lobes having an outer surface that defines a second lobe profile,
• wherein the first and second rotors formed from metal having a coefficient of thermal expansion from about 1 (10−6 in/in*K) to about 13 (10−6 in/in*K), wherein an inner surface of the booster housing includes a coating including at least one of an abradable coating or a formable coating, and wherein a portion of the coating has a thickness from about 0.001 inches to about 0.025 inches and a surface roughness from about 125 Ra to about 1000 Ra.